Computing device for photographic cameras



Jne 17, 1947. A, SiMMON 2,422,316

COMPUTING DEVICE FOR PHOTOGRAPHIC CAMERAS Original Filed May 25,' 1945 9 Sheets-Sheet ll A hrrd .ffm man June 17, 1947. A S|MMON 2,422,316

COMPUTING DEVICE FOR PHOTOGRAPHIC CAMERAS Original Filed May 25, 1945 9 Sheets-Sheet 2 OSO June 17, 1947. A. slMMoN COMPUTING DEVICE FOR PHOTOGRAPHIC CAMERAS Original Filed May 25, 1945 9 Sheets-Sheet 3 June 17,v 1947. A. slMMON COMPUTING DEVICE FOR PHOTOGRAPHIC CAMERAS original FiledMay 25, 1945 9 Sheets-Sheet 4 June 17, 1947.

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COMPUTING DEVICE`FOR PHOTOGRAPHIC CAMERAS Original Filed May 25, 1945 9 Sheets-Sheet 6 June 17, 1947.

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F/gf 9 VV/r//////////////////////////////////////////// .Q 6 F m Original Filed May 25, 1945 9 Sheets-Sheet 9 5.21 mxmmz 3 mm1/tom m40/7 Patented June 17, 1947 COMPUTING DEVICE FOR PHOTOGRAPHIC CAMERAS Alfred Simmon, Jackson Heights, N. Y., assignor to Simmon Brothers, Inc., Long Island City, N. Y., a corporation of New York Original application May 25, 1945, Serial No. 595,702, now Patent No. 2,418,370, dated April Divided and this application March 29, 1946, Serial N0. 657,990

1 Claim.

This is a division of an application for patent, Serial #595,702, led May 25, 1945, now issued as No. 2,418,370 on April 1, 1947, and has for its object to provide a computing device for photographic purposes, which coordinates the various factors aiife'cting a photographic exposure and indicates the required light intensity which must be reflected by the scene to be photographed in order to render a correct exposure for a given set of exposure controlling factors. Exposure controlling factors in this sense are the lter factor, the diaphragm ratio of the lens or the so-called F number, the lm sensitivity, and the exposure time.

A further object of this invention is to provide a computing device of this character which can be made part of a camera and is adapted to be in operative relation with a built-in exposure meter. Thus the exposure meter indicates the actual value of the light reected by the scene to be photographed, the computing device indicates the light required for a given set of exposure controlling factors, and a correct exposure is being obtained whenever the two light values are equal. While this application for patent describes in detail a camera and a meter with which the aforesaid computing device can be used, this is only by way of illustration and better to explain the working of the device. Application Serial #595,- 702 fully covers the camera itself.

In the preferred embodiment of this invention the means to adjust the various exposure controlling factors of the camera are in operative engagement with the means to adjust the corresponding indicators of the computing device so that, for example, the actual setting of the lens diaphragm corresponds to the value indicated by the diaphragm scale of the computing device.

The relations determining the required light intensity are well known and quite simple. The required light intensity increases in direct proportion to the lter factor, if a, iilter is being used, and it increases with the square of the diaphragm ratio of the lens, the so-called F number. The required light intensity increases in inverse proportion to the iilm sensitivity and in inverse proportion to the exposure time as determined by the shutter of the camera. The following formula reflects these conditions:

Required light intensity= C t t X Filter factor X (diaphragm rat1o)2 ons an Film sensitivityX exposure time Or in logarithmic terms:

Log L=log C'-|-log IPH-log D2-log Slog T As can be noted this formula gives the value of the required light intensity as a function of four variables. In order to coordinate these four variables, numerous devices have been suggested in the past. Usually, some of these values were combined by means of mechanical sliderule-like devices and some of the other values were taken into account by electrical resistors or by means which may be called optical resistors, which decreased the reading of the exposure meter in proportion, or in inverse proportion, as the case may be, to some other magnitudes. Optical resistors in this sense are, for example, grey lters or adjustable diaphragme in front of the photoelectric cell. The objectionable feature of all these resistors is that they reduce the reading and therewith the sensitivity of the meter and that very often the meter indications become, therefore, small, diiiicult to read, and inaccurate. Electrical resistors have, furthermore, the disadvantage of getting frequently out of order since they must comprise very many turns of exceedingly thin wire.

Compared to this prior art, this invention has the advantage that the electric meter is always used at its maximum sensitivity and that always the largest possible movement of the pointer is being observed. It has the further advantage that no mechanical, electrical, or optical connection exists between the meter and the other parts of the camera. The computing device itself is quite simple and consists of a relatively small number of parts. 1t is very compact and, in particular, the nal scale indicating required light values does not becomelonger than the scale of any of the yiour exposure controlling factors.

In the accompanying drawings,

Fig. 1 illustrates in diagrammatic form the principle of the computing device forming the subject matter of this invention;

Fig. 2 illustrates a more refined form of the device;

Fig. 3 shows a plan view of a camera with a built-in exposure meter and the computing device;

Fig. 4 is a front view of the same;

Fig. 5 is a cross sectional View along the plane of line 5-5 of Fig. 4, the operating levers being shown all in one plane for sake of clarity;

Fig. 6 is a cross sectional View along the plane of line 6-6 of Fig. 5;

Fig. 7 is a cross sectional view along the plane oi line -l in Fig.

Fig. 8 is again a front View of the camera but without a protective cover so that certain shafts and levers become visible which actuate the adby projections attached to slide 32. The bearings in which slide 4Q slides must have a very low amount of friction and, consequently, if for example, slide 32 is moved, this movement, in turn, being due to a movement of either' slide 23 justments of the shutter and the diaphragm, reo or slide '10 will move by half the amount oi spectively; the travel of slide 32 or, if one assumes that the Fig. 9 is a cross sectional view along the plane movement of slide 32 was due to a movement of of line 9 9 in Fig, 4 showing the computing deslide the travel oi slide 4Q will be one-quarter vice as actually incorporated into the camera; 10 of the travel of slide 23, Slide 43 is equipped Fig. 10 is substantially the same as Fig. 3, but with a mark 45, which indicates on scale L36 the showing modified means for the setting of the required light intensity for a correct exposure. filter factor and the film sensitivity; and As can be seen, the values of the upper two Fig. 1l show a slight modification of the mechscales increase from left to right, but the values anisrn used in connection with the camera in for the two lower scales increase from right to accordance with Fig. 10. left. Therefore, an increase in either the filter Like numbers of reference denote similar parts factor or the diaphragm ratio will cause an inthroughout the several views and the following crease in the required light intensity as indispecication. cated by mark (45, but an increase in the value The principle of the computing device can be of the exposure time or the nlm sensitivity scales best understood with the aid of Fig. 1. Four wiil cause a decrease oi the required light inslides 2l, 22, 23 and 24 are provided which may tensity as indicated by mark 45. Due to this arbe moved individually by the operator in either rangement, the last two magnitudes are being direction. Each of these slides is equipped with counted negatively when adding up the movea mark 26, 27, 28 and 29, respectively. These 25 ments oi the four slides, as they affect the travel marks cooperate with four Xed scales which of the result slide 49, The movemeilts of all are calibrated in terms of lter factors, diaphragm slides can now be computed:

Movement of- Movement oi- Movement ofl iii3111111111:. hide Sel-0g Flog D2 Slide el-Mg FFM l?, --"li Mii S ii; i .T iiiiiiiiilislid 23=gm TEE-S ratio or actually the square of the diaphraghm In other words, the movement of slide is proratio, emosure time, and lm sensitivity. The portional to the desired function, and the relines on these scales are spaced logarithmically, sult scale 46 need not be longer than one-quari. e., the distance of any line from the 40 ter of the sum of the four input scales, or starting point of the scale is proportional to approximately as long as any of these input the logarithm of the value indicated by said line` scales. This is very important for compactness The simplest way to accomplish this, and one and a peculiar advantage of this arrangement. which conforms very well with current photo- `Other devices proposed for this purpose, for graphic usage, is to arrange the values on these example, a flexible ribbon running over a numscales in geometric progression, each line indiber of pulleys, require an excessively long result" eating twice the value indicated by the precedscale. ing line. Two more slides 3l and 32 are It is most expedient to arrange the scale 4B mounted between slides 2l and 22 and slides 23 which indicates the required light intensities, in and 24, respectively. Slide 3l carries a double adjacent arrangement to the exposure meter 50 ended pivoted lever 33, and slide 32 carries an 50 and provide lines on the exposure meter dial identical pivoted lever 34. As can be seen, slide whereby identical light values of scale 46 and 2l has tivo projections 35 and 3B forming a gap exposure meter 52 are being connected. In this engaging one end of lever 33. In an identical manner, the arrangement immediately indicates manner, slide 22 has two projections 3l and 38 to the operator whether the required light intenwhich form another gap engaging the other end sity is larger, equal, or smaller than the actual of lever 33. The bearings, in which slides 2l and light intensity as indicated by the meter. For 22 slide, must have a relatively high amount of a correct exposure, the operator has nothing friction, but the bearings in which slide 3l slides more to do than to adjust at least one of the have somewhat less friction. Consequently, if exposure factors in such a manner that mark 45 the operator moves, for example, slide 22, slide and the pointer of the exposure meter 50 are 2l will remain stationary and the fulcrum of the in register. double ended lever 33, and therewith the entire The mechanical arrangement as shown in slide 3l, will move by half the amount of travel Fig. 1, leaves in practice something to be desired of slide 22. since obviously the angle of rotation that can be The movements of slides 23 and 24 are coor- 65 covered by the pivoted levers 33, 34 and 4l is dinated in precisely the same manner and if, for limited. This, .in turn, limits the possible moveexample, the operator chooses to move slide 23, ment of all seven slides and, furthermore, makes slide 2A will remain stationary and slide 32 will the construction of a compact device difficult move by half the amount of the movement of if not impossible. A solution which is identical slide 23. in principle, but more practical becomes possible Mounted between slides 3l and 32 is a seventh by considering the two ends of the double ended slide 4B which carries the double ended pivoted levers 33, 34 and 4I, respectively, as two diametlever 4l. One end of this lever 4lengages a gap rically opposed teeth of a primitive gear and by formed by projections attached to slide 3l, and considering in like manner, for example, the prothe other end of lever 4l engages a gap formed 75 jections 35 and 36 attached to slide 2l as two teeth of a rudimentary gear rack. By su'bstituting a complete gear rack for these two projections and by substituting complete gears for the three pivoted levers, one arrives at the design shown in Fig. 2. The four slides 6|, 62, 63 and 64 correspond to the four slides 2|, '22, 23 and 24, respectively. Each has a mark 66, 61, 68 and 69 which cooperates with a scale fdr the lter factor, diaphragm ratio, exposure time and lm sensitivity, respectively. Between slide 6| and 62 is positioned'slide 1| which carries a rotatable gear 63 which is in mesh with the teeth of slides 6| and 62. In like manner, a slide 12 carrying a gear 14 is positioned between slides 63 and 64, gear 14 being in mesh with the teeth of slides 63 and l64. A seventh slide carrying a gear 8| is positioned between slides 1| and 12, gear 8| being in mesh with the teeth of slides 1| and 12. Slide 80 is equipped with a mark 85 which indicates on a scale 86 the required light intensity. This scale 86 is again in adjacent arrangement to a meter 90 which indicates the actual light conditions, and again a correctly exposed picture will be obtained as soon as the operator brings mark 85 and the pointer of meter 90 into register. The movements of the various slides have exactly the same relation to each other as in Fig. l, i. e., the travel of slide 1| equals half the sum of the travel of slides 6| and 62, the travel of slide 12 equals half the sum of the travel of slides 63 and 64 and iinally the travel of slide 80 equals half the sum of the movement of slides 1| and 12. The scales which indicate the respective positions of the four input slides are again arranged in the manner described above, i. e., the values of the upper two scales for the filter factor and the diaphragm ratio, respectively, increase from left to right and the values of the two lower scales of the exposure time and iilm sensitivity, respectively, increase from right to left. Merely as an example, the seven slides are shown to be equipped with elongated slots which engage each two fixed pins thereby permitting a slidingr straight line movement of each slide from right to left and vice-versa.

A camera equipped with a computing device built according to this invention is shown in Figs. 3 to l1. In the interest of clarity and simplicity, certain parts of this camera which do not form part of this invention have either been omitted, such as a range and view nder, or they have been shown rather diagrammatically, such as a focusing device of which only the actuating knob or handwheel 99 can be seen.

Camera housing While the camera housing in the drawings has been shown as of one piece construction, it is in reality, of course, suitably sub-divided so as to permit convenient manufacture and assembly. This housing consists essentially of an inner part ||l| shaped like a stepped cone forming a light chamber, confining the light rays passing through lens |09 and impinging upon the sensitized photographic film |32, and an outer shell comprising a top wall |02, a bottom wall |03, a left side wall |04, a right side wall |05, a front wall |06 and a rear wall |01. Underneath the top wall |02, and parallel thereto, is a dividing wall |08 which serves to support the various slides of the computing device.

The top wall |02 has a number of elongated slots which are preferably covered by glass or a transparent plastic material and through which the marks associated with the various slides of the computing device are visible. The various scales cooperating with these marks are engraved upon, or otherwise aflixed to, the top wall of the camera. The top wall also carries the electrical exposure meter 0 with its pointer and its dial ||2, see Fig. 3.

The front wall |06 is adapted to receive a shutter ||5 which, together with a camera lens |09, forms, as usual, an integral unit, Figs. 5 and 7. The shutter is, by way of example only, a typical between the lens shutter having a diaphragm adjusting ring and a speed adjusting ring concentrically disposed and coaxial with the camerav lens. 'I'.wo lugs ||8 and ||9 are fastened to the two rings controlling diaphragm and shutter speed, respectively, and other elements to be described later are attached to these lugs. In front of the front wall |06 is a safety cover |20, preferably made from sheet metal, which has a circular aperture for the lens, but which otherwise covers the shutter and its actuating mechanism. Attached to this safety cover are two guides |2| adapted to receive a lter |22 with its supporting structure |23, Figs. 4, 5 and '1. A photo-electric cell |24 which supplies current to the meter ||0 may also be fastened to part |20.

The bottom wall |03 and the right side wall |05 have no noteworthy features and are merely shown for the sake of completeness. The left side wall |04 is curved and has four elongated slots permitting the movement of certain levers which actuate the slides of the computing device and the diaphragm and speed adjustment of the shutter, Figs. 3, 4, 5 and 6.

The rear wall is adapted to receive an exchangeable roll lm magazine |30. This magazine contains two lm spools 3| and a iiexible sensitized nlm |32, which is, during operation, wound from one iilm spool onto the other in the usual manner. A knob |33 is provided for this purpose. The film magazine also comprises, in reality, a dark slide and means to keep the film as nearly nat as possible, but since these features do not form part of this invention, they have not been shown.

Computing' device The computing device as actually incorporated in the camera can be seen in Figs. 7 and 9. The actual design, as seen in Fig. 9, corresponds very closely to the diagrammatic drawing in Fig. 2 and has, therefore, been assigned the same reference numbers to corresponding parts. The only departure is the shape of the intermediate slides 1| and 12 which are now U-shaped, one leg of the U carrying the gears 13 and 14, respectively, and the other leg being equipped with teeth forming gear racks. This obviously does not affect the principle of the computing device, but merely makes a more compact arrangement possible since new gear 8| does not have to be excessively large and since it is now possible to arrange all parts more nearly in one common plane.

Means to shift slides of computing device In order to enable the operator to shift the slides of the computing device conveniently, an arrangement has been provided for each slide which can best be seen in Fig. 6. It comprises a rotatable lever |52 with a handle which protrudes through one of the aforementioned elongated slots of the left camera side wall |04, said lever having a lug |42 which, by means of a connecting rod |43 moves another lug |44, which in turn protrudes through an elongated slot in wall |08 and is fastened to one of the 4 input slides of the computing device, in this instance, for example, to slide 62, indicating the diaphragm ratio. Similar' arrangements are provided for the other three input slides, as can be seen in Fig. 5, lever |50 actuating the. slide for the film sensitivity, lever actuating the slide for the exposure time, and lever |53 actuating the slide for the lter factor. The stepsl of the above mentioned stepped cone or light chamber serve as pivots for these 4 levers which swivel concentrically with respect to the axis of the camera lens. This concentric arrangement' is not strictly necessary, but it is compact and the large bearing diameter provides more or less automatically the desired amount of friction in the slide adjusting mechamsm.

M cans to adjust tteflens diaphragm and the shutter sneed It is desirable to adjust the actual diaphragm opening of the lens and the actual speed adjustment of the shutter simultaneously7 with the adjustment of the corresponding slides of the computing device, since otherwise the operator would have to make two adjustments for each of these factors which is not only inconvenient, but which would make mistakes possible sinceA the operator may not make both adjustments properly et all times. The diaphragm and speed settings usually do not follow any discernible laws and, therefore, cams of suitable configuration must be interposed into the adjusting mechanism at some place in order to provide the necessary corelaticn. An embodiment of this idea is shown in Figs. 6 and il. Lever |52 which, as explained above, controls the position of the diaphragm indicating slide 52, carries a cam |60. Sliding on this cam is cam following roller |-E| which is attached to a lever |52. This lever is fastened to a shaft |53' which runs parallel to the lens axis, see Fig. 5. The front end of this shaft penetrates the front wall |95 of the camera. This front end can be seen in Fig. 8 which shows the camera with the safety cover |20 removed. The front end of shaft IES is flxedly attached to a lever |54 which, by means of connectingv rod |55, actuates lug H8 which. in turn, moves the diaphragm adjusting ring of the lens and shutter assembly. .A very' similar arrangement is used for the speed setting of the shutter. Lever |5| is equipped with av cam 519,. a cross-section of which can be seen in Fig, This cam cooperates with a cam fol.- lowing roller lll attached to a lever |'=2 which is not shown but has a shape very similar to that of lever |62. rhis lever is attached to a shaft H3 parallel to the lens axis and very similar to shaft |83, but longer. Its position with respect to the other partsof the camera can be seen in 6 and 8. Its front end carries a lever |14 ehcorresponds to lever |64 of the diaphragm ad sting mechanism,l but is arranged in a plane slightly behind. it so as to avoid interference. Lever il@ actuates, by means of a connecting 515, lug i9 which, in turn, is attached to the speed adjusting ring of the shutter |25. Two s rings lt and are provided which bias the diaphragm adjusting mechanism and the shutter speed adjusting mechanism, respectively, in sue-h e way that the cam following rollers 15| and Vil are always in contact with their respective cams |60 and VIS.

Means to coordinate film factor and film sensitivity To make the camera as foolproof as possible, it

is desirable to provide means to facilitate the, correct adjustment of theV slides for the filter factor and the film sensitivity, respectively. Ref to Fig. it will be noted that the filter by a filter mount 23, which in be inserted into the grooves of the two ities li as described above. The upper is filter mount carries an abutment |86 ws a legend describing the filter and a which, when the filter is properly the camera, shows on the filter scale on tcp of the camera the proper ical filter factor for this filter. The operator then merely moves lever |53 until the mark of the filter factor slide of the computing device and the mark on the abutment |88 of the filter mount are in register as shown in Fig. 3.

On tcp of the camera itself, opposite the first line of the filter factor scale, is a similar mark which is not visible as soon as any filter is inserted into the camera, but becomes visible whenever the camera is being used without any filter. This mark is shown in dotted lines in Fig. 3. This reminds the operator to move lever |53 back il the movable mark of the lter factor indieating slide also points to the first line. In other words, both visible marks must, at all times, be in register.

Similar means are provided for the convenient adjustment of the computing device for various hlm sensitivities. rThe exchangeable roll film magazine |35V carries a nameplate with a mark, descrising the film with which this magazine is loaded. When the roll film magazine is inserted into the camera this nameplate with its mark is in adjacent arrangement to the film sensitivity scale on top of he camera and the mark points at that line of the scale which corresponds to the film sensitivity of the film in the magazine. The operator then moves lever l5!! until' the sliding mark of the nlm sensitivity slide cf the comdevice is in register with the fixed mark of the roll film magazine.

The entire arrangement can be seen in Fig. 3. It is simple; it provides the operator, at a glance, with all pertinent information on thel adjustments of the camera, and the juxtaposition of the two respective marks for the lter factor and the nlm sensitivity is a very effective and substantially foolproof reminder for the operator. However, a still more nearly foolproof arrangement can be made and is shown in Fig. l0 which shows a plan view of a camera, very similar to Fig. 3 except for certain modifications which are about to be described. Instead of mark 66 indicating the filter factor on the filter factor scale, there is an actual projection |93 protruding through the elongated slot in the top wall of the camera housing. This slot is, of course, no longer closed by a transparent window. A similar projection |9| is provided on the abutment |83 of the filter mount |22. The filter factor indicating slide is biased by a spring |92 which is shown in Fig. 11 and has, therefore, the tendency to return automatically to the lowest setting on this filter factor scale, i. e., toV line #1, and it will assume this position in the absenceV of a lter. However, shouldL the operator decide to use a filter, he merely moves the projection as far to the right as necessary, by lifting handle |53, inserts the filter mount and releases handle |53, whereupon projection |93 will automatically move back until it meets the projection |8| on the filter mount. Projection |90 has a shape which will not permit the correct insertion of the filter mount into the camera unless the operator proceeds in the manner described.

An identical arrangement can be provided for the automatic adjustment of the film sensitivity slide 64 of the computing device. This slide 64 is now, instead of a mere mark B9, equipped with an actual projection |95 which protrudes through the elongated slot on top of the camera housing and which cooperates with a similar mark |96 fastened to the exchangeable roll nlm magazine |35. The slide 64 is again biased by a spring |91, shown in Fig. 11. The operator again proceeds by rst shifting slide 64 with its projection |95 suiciently far towards the right, whereupon he inserts the roll film magazine and releases handle |50. Spring |9'l then will cause slide 64 with its projection |95 to return until projection |95 meets projection |95. In other words, the lm sensitivity slide of the computing device will in this manner automatically assume the correct position. The mark |95, which is allxed to the roll film magazine, is shaped in such a manner that correct insertion of the magazine is not possible unless the operator shifts mark |95 first in the described manner.

Sometimes, particularly in the case of relatively inexpensive carneras, it may be advisable to keep the appearance of the camera as simple as possible. In this case, the two scales for the filter factor and film sensitivity may be omitted, and merely the coacting projections |90 and |9|, and |95 and |96, may be provided. The proper adjustment of the computing device is automatin cally assured by this interlocking arrangement, and the operator is very often not interested in the exact numerical values of lter factor and film sensitivity, so long as correct exposures are being obtained.

The operation of the camera and the coaction of the various parts can now be fully understood from the description above. Depending upon the type of picture which the operator plans to take, he selects a film magazine loaded with a suitable type of film and inserts it into the camera. If the camera is equipped with an interlocking arrangement, such as shown in Fig. 10, the film sensitivity slide of the computing device will automatically be in the correct position after insertion of the magazine. With the arrangement of Fig. 3 the operator moves lever |50 until mark 69 is in register with the corresponding mark on the lm magazine. The operator then decides whether a filter may advantageously be used and, if necessary, selects a, suitable one and inserts it into the camera. With an interlocking arrangement such as shown in Fig. 10, the lter factor slide of the computing device assumes automatically the correct position. With a device such as shown in Fig. 3, the operator moves handle |53 until mark B6 is in register with the corresponding mark on the filter mount.

The next step is to adjust the exposure time of the shutter and of the computing device by moving handle |5|. The most favorable exposure time depends upon a number of factors, but more than anything else, upon the speed with which the object to be photographed moves. It is usually advantageous to choose the longest possible exposure time compatible with the speed of a moving object because this permits the use of the smallest possible diaphragm stop, thereby assuring the best possible depths of focus.

The camera is then pointed at the scene to be photographed, usually with the aid of a view lnder which, however, as explained above, is

not shown on the drawings. Light reflected by the scene impingesupon the photo-electric cell |24 and causes it to generate an electrical current which is measured by the meter 0 on top of the camera. The pointer may, for example, assume the position shown in Fig. 3. The operator then adjusts the diaphragm, and the diaphragm slide of the computing device, by moving handle |52 until mark 85 is in register with the pointer of the indicating meter. This indicates that all factors have been chosen in such a way that the required light value, as computed by the computing device, equals the actual light value as measured by the exposure meter. The camera is now ready for a correctly exposed picture.

An experienced operator will usually choose his factors in such a way that, by merely moving the diaphragm setting, mark can be brought into register with the meter pointer without difficulty. Under certain circumstances, however, this may be impossible; for example, an inexperienced operator may choose a slow film, a dense filter, and a short exposure time under unfavorable light conditions and then, even with the diaphragm wide open, the required light intensity may still be larger than the actual intensity as indicated by the meter. In other words, mark 85 will be to the right of pointer This means that no correctly exposed picture is possible under the circumstances and the operator has to change some of the exposure controlling factors. Usually it is most convenient to use a longer exposure time, but should this not be suflicient, the operator has to use a faster film, or a less dense filter, or omit the filter altogether.

In the same manner, the operator may choose inadvertently a very fast iilm, no filter, and a relatively long exposure time under extremely bright light conditions, for example, at the seashore in bright sunshine. It is possible that under these conditions the actual light intensity may consistently be higher than the required intensity so that over-exposure would result. This is immediately indicated by the fact that mark 85 cannot be brought in register with point but remains always to the left of it. Again, some exposure factors would have to be changed; for example, a higher shutter speed may have to be chosen. Since, under ordinary conditions, the adjustment of the diaphragm will be made last, i. e., almost immediately before the actual exposure, a larger and more conspicuous handle |52 has been provided for this purpose.

I wish to emphasize that this description covers merely a preferred embodiment of the invention and a method of applying its principles to a camera, and that many details may be freely changed without departing from its spirit. For example, while I have consistently .shown stationary or fixed scales attached to the camera housing and movable marks attached to the various slides of the computing device, this arrangement may very well be reversed, i. e., the scales may be attached to the slides and stationary marks may be aiiixed to the camera housing. It has already been mentioned that for the purpose of this invention the two ended pivoted levers, such as shown in Fig. 1, may be considered the mechanical equivalent of gears, and that a slide equipped with two projections forming a gap betwen themselves may be considered the mechanical equivalent of a gear rack. The cam and lever arrangement illustrated in Fig. 6 may also be reversed. As shown, the slides of the computing device, for example, slide 62, Fig. 6, are actuated through connecting faam-gaie rods M3 by lugs |52 aiixed to the adjusting levers, for example, |52, and the levers adjusting the diaphragm |54 and the shutter speed |14, respectively, are actuated by cams |60 and |10, also aixed to said levers. Obviously, the opposite arrangement, i. e., the actuation of the computer slides by cams and the actuation of the diaphragm and speed adjusting mechanism by connecting links, is the obvious mechanical equivalent of the arrangement shown and should be construed to fall within the scope of this invention. The means to actuate the slides of the computing device do not necessarily have to be constructed in the manner shown and, particularly, the actuating levers |50, |5l, |52 and |53 do not have to rotate on bearings which are concentric with the lens axis. While I have shown an exchangeable roll iilm magazine, it Will be obvious that a magazine containing any other type oi sensitized material such as cut or pack lms would be equally applicable. Variations 'of this Acharacter and obvious mechanical equivalents of this type shall be construed to be covered by the appended claim.

What I claim as new is:

A device to compute the light intensity required for correctly exposed picture in a photographic camera from a given set of values for the filter factor, diaphragm opening, shutter controlled exposure time vand film sensitivity, respectively, said device comprising a supporting structure and four slides, said slides movable individually and independently along straight vand parallel lines, each of said slides having a mark, a stationary scale on said structure for eachof said slides and cooperating with the mark of its slide, the Vfirst of said scales calibrated in logarithmically spaced 12 values of `iilter factors, the second vof said scales calibrated in values of the ratio of the focal length of the camera lens divided by the eiective diaphragm diameter of said lens, the spacing of said values being in proportion to the logarithms of their squares, the lindicated values of both scales increasing in the same direction, the third of said 'scales calibrated in logarithmically spaced values of the exposure time of the camera shutter, and the fourth vof said scales calibrated in logarithmically spaced values of the film sensitivity, Ythe indicated values of said last two scales increasing in the opposite 'direction to that of the rst two scales, each 'of said slides equipped with avgear rack, the racks of one pair ofslides facing each other, and racks of the other vpair of slides facing each other, a gear between the racksof the rst pair and 'in 'mesh with both, a iifthlslide, said gear mounted rotatably upon said fifth slide, a second gear between the racks of the second pair Aand in mesh vwith both, a sixth slide, said second vgear mounted rotatably upon said sixth slide, said fifth 'and sixth slides movable along straight lines parallel to the -lines of movement of 'the first four slides, landeach equipped with a gear rack, said racks lfacing yeach other, a third gear between the racks of said fifth and sixth slides and in mesh with both, a seventh slide, said third gear mounted rotatably upon said Seventh "Slide, fsaid seventh Slide movable along a straight line parallel lto :the 4movement `of all other slides, and a markon said seventh slide cooperating with as'tationary scale `on said-stricture calibrated in logarithmically spaced values of required light intensities.

SIMMON. 

